In general, a liquid crystal display (LCD) includes a display panel in which a plurality of pixels are arranged in a matrix form, and a backlight unit which is attached on the back side of the display panel and has light sources for radiating light to the pixels. The LCD displays an image according to driving voltages provided to the pixels and intensities of light radiated from the light sources.
Image quality of the LCD depends on a contrast property. A method of controlling a data voltage that is applied to a liquid crystal layer to modulate light transmission has a limitation in improving the contrast property. In order to improve the contrast property, a backlight dimming method of adjusting the brightness of a backlight according to an image has been proposed. The backlight dimming method includes a global dimming method of adjusting the brightness of an entire display area, and a local dimming method of partially adjusting the brightness of display areas. According to the local dimming method, an LCD is controlled such that blocks have different dimming levels. Also, an LCD based on the global dimming method is controlled under the same dimming level since the LCD is configured as a single block. The global dimming method can improve dynamic contrast measured between a frame and the previous frame. The local dimming method can improve static contrast by locally controlling the brightness of display areas in a frame period. The global dimming method has difficulties in improving the static contrast.
Meanwhile, an organic light emitting diode (OLED) display, which has attracted attention as a next-generation flat panel display, requires no backlight unit since a fluorescent organic compound itself radiates light, unlike liquid crystal. In the OLED display, light-emitting devices configuring pixels of a display panel control the intensity of light.